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Visualizing Environmental Science
The Ocean and Fisheries
Chapter 11
Chapter
Chapter77
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Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
The Global Ocean
• Patterns of circulation
– Winds over the ocean produce currents
• Mass movements of surface-ocean water
• Gyres- large circular ocean currents
– Clockwise gyre in North Atlantic
• Coriolis effect
– Influences the paths of shallow
ocean currents
– Earth’s rotation causes currents to swerve
» Right in Northern Hemisphere, clockwise movement
» Left in Southern Hemisphere, counterclockwise
movement
© 2014 John Wiley & Sons, Inc. All rights reserved.
Patterns of Ocean Circulation
• Ocean conveyor belt
– Moves deep, salty sea water from higher to lower
latitudes water warms up
– Affects regional and global climate
– Delivers heat from
tropics to Europe
© 2014 John Wiley & Sons, Inc. All rights reserved.
Normal vs. El Niño (ENSO) Conditions
© 2014 John Wiley & Sons, Inc. All rights reserved.
The Global Ocean
• ENSO
– 1997–98 caused 20,000 deaths and $33 billion in
property damage
• Snows in Western U.S., ice storms in Eastern Canada
• Torrential rains in Peru, Ecuador, California, Western Europe
• Droughts in Texas, Australia, Indonesia
• TAO/TRITON array
– Used to monitor sea surface temperatures and winds
– Used to forecast and better understand ENSO events
© 2014 John Wiley & Sons, Inc. All rights reserved.
Major Ocean Life Zones
© 2014 John Wiley & Sons, Inc. All rights reserved.
Tidal Zones
© 2014 John Wiley & Sons, Inc. All rights reserved.
Major Ocean Life Zones
• Benthic environment
– The ocean floor, which extends from the intertidal zone to the
deep ocean trenches
– Consists of sediments (sand and mud)
– Burrowing animals
• Bacteria, worms, clams, etc.
– Corals: soft-bodied animals, similar to jellyfish
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Live in hard cups or shells of calcium carbonate
Accumulated skeletons produce coral reefs
Found in warm, shallow waters
Require light for symbiotic zooxanthellae
High productivity even in poor nutrient waters
Ecologically important: habitat; protect coastlines from erosion
A threatened ecosystem: Pollution from ocean dumping and coastal
pollution, silt washing downstream from clear-cut forests is
smothering reefs, overharvesting, introduction of nonnative species,
bleaching where stressed corals expel zooxanthellae (an event
correlated with warming ocean waters), overfishing of top predators,
damage from recreation.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Major Ocean Life Zones
• Benthic environment
– Sea grasses
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Flowering plants adapted to live in sea water
Quiet temperate, subtropical, and tropical waters
High primary productivity
Ecologically important
– Stabilize sediments, reduce erosion, provide food and habitat for marine organisms
– Kelps
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Largest and most complex of all seaweeds
Brown algae
Common in cooler temperate marine waters
Primary food producers for kelp “forest” ecosystem
Provide habitat for many marine organisms
– Tubeworms, sponges, sea cucumbers, clams, crabs, fishes,
sea otters, and sharks
• Very diverse ecosystem
© 2014 John Wiley & Sons, Inc. All rights reserved.
Major Ocean Life Zones
• Neritic province
– Part of the pelagic environment that overlies the ocean
floor from the shoreline to a depth of 200 meters
– Organisms are floaters (plankton) or swimmers (nekton)
– Euphotic zone: upper level of neritic zone
• Sufficient light to support photosynthetic organisms
• Phytoplankton are basis of food webs
• Zooplankton feed on phytoplankton
• Plankton-eating nekton consumes zooplankton
• Carnivorous nekton consumes plankton-eating nekton
© 2014 John Wiley & Sons, Inc. All rights reserved.
Major Ocean Life Zones
• Oceanic province
– Cold waters, high pressure, no light
– Life adapted to darkness and scarce food
• Drifting or slow swimming, reduced bone & muscle
mass
• Light producing organs to locate mates or prey
• Depend on ‘marine snow’ (organic debris from upper
layers of ocean)
• Filter feeders, scavengers, predators
• Many large invertebrates, e.g., giant squid
© 2014 John Wiley & Sons, Inc. All rights reserved.
Human Impacts on the Ocean
• Marine pollution and deteriorating habitat
– Paradox: ocean provides food but is used as
dumping ground
– Pollution increasingly threatens fisheries
– 80% of ocean pollution comes from land activities
© 2014 John Wiley & Sons, Inc. All rights reserved.
Ocean Pollution has Few Controls
• Discarded plastic flotsam
and jetsam are becoming a
ubiquitous mark of human
impact on the oceans.
• 6 million metric tons of
plastic are tossed from
ships every year into the
ocean, where they ensnare
and choke seabirds,
mammals, and even fish.
• Estimated 8 plastic pieces
for every 1 zooplankton
10-13
Human Impacts on the Ocean
• World fisheries
– Valuable food resources
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90% of world’s catch is fishes
6% is clams, oysters, squid, octopus, and other molluscs
3% is crustaceans: lobsters, crabs, shrimp
1% is marine algae
– World’s annual fish harvest
• 1950 - 19 million tons
• 2000 - 95 million tons
• 2011 - 90 million tons
© 2014 John Wiley & Sons, Inc. All rights reserved.
Human Impacts on the Ocean
• Problems and challenges for the fishing industry
– No nation has legal claim to open ocean
• Resources are susceptible to overuse and degradation
(Tragedy of the Commons)
– Many species have been harvested to the point where
their numbers are severely depleted
• Unstable for marine species that rely on them as part of
food web
• At least 75% of world’s fish stocks are exploited,
overexploited or depleted
– Growing human population requires protein
– Technological advances allow efficient catch, removing all fish
from an area
– 25% of all is bycatch (unintentionally caught, then discarded)
© 2014 John Wiley & Sons, Inc. All rights reserved.
Human Impacts - Aquaculture
• Net pens anchored in nearshore areas allow spread of diseases,
escape of exotic species and nonnative genes (GMO fish), and
release of feces, uneaten food, antibiotics, and other pollutants into
surrounding ecosystems. Plus these fish are still fed with wild caught
fish.
Human Impacts on the Ocean
• Offshore extraction of mineral and energy
resources
– Large deposits of minerals lie under the sea floor
• Manganese nodules
• Petroleum
– Major source of energy
– Major threat to fishing
© 2014 John Wiley & Sons, Inc. All rights reserved.
Human Impacts on the Ocean
• Climate change
– Potential disruption of the ocean conveyor belt,
which transports heat around the globe
– Climate warming could shut down conveyor belt within a
decade
» Could cause major cooling in Europe
» Major warming in other parts of the world
» Would not sequester CO2 into ocean  more CO2 in
atmosphere  more warming  more weakening of belt
– Acidification of the ocean
© 2014 John Wiley & Sons, Inc. All rights reserved.
Addressing Ocean Problems
• Problems are complex and require complex solutions
– U.N. Convention on the Law of the Sea (UNCLOS) -1994 - 157 countries
have ratified
• Protecting ocean resources
– U.N. Fish Stocks Agreement - 1995
• Regulates marine fishing
– Fishery Conservation and Management Act (1977)
• Protect essential fish habitat for 600 species
• Reduce overfishing, rebuild populations, minimize bycatch
• Fishing quotas, restrictions on fishing gear, limits on number of fishing boats,
closure of fisheries during spawning
© 2014 John Wiley & Sons, Inc. All rights reserved.
Addressing Ocean Problems
• Future actions
– Establishment of “no-take” reserves
– Substantial reduction of fishing fleet
– Remove subsidies of fishing industry
– Adopt an ecosystem-based approach to manage
ocean environments
• Focus on preserving the health and function of the
entire marine ecosystem
• Establish networks of fully protected marine reserves
• Less than 5% of U.S. marine environments have been
protected, with great success
© 2014 John Wiley & Sons, Inc. All rights reserved.
Case Study
• The dead zone in the Gulf of Mexico
– N and P runoff from Mississippi River
• Algae grow rapidly, dead algae sink to bottom and
decompose, deplete water of O2 (hypoxic zone)
– Only anaerobic bacteria thrive there
© 2014 John Wiley & Sons, Inc. All rights reserved.
Case Study
• March to September, worst June-August
• Climate change is making dead zones worse,
even without runoff
• Threaten biodiversity and coastal fisheries
© 2014 John Wiley & Sons, Inc. All rights reserved.